My dear Sir

I thank you much for your information on sexual differences with the pretty little sketch of the male crab, & for the great trouble which you have taken in copying the long extract from Claus,² All such facts interest me much. I shall also be very glad for answers to any of my questions on the expression of negros.³ Your additions about the self-sterile orchids are particularly valuable, & I shall give an abstract of all the information which you have so kindly given me.⁴ The comparison of the pollen with that when species are crossed makes the facts much more curious.⁵ The analogous cases which have been observed in Europe I have always attributed to the unnatural condition under which the orchids were grown; but it now appears that this is an error; I fear however that I shall not be able to alter the place in my book where I give these facts.⁶ As D^r Hildebrand in experimenting on Corydalis used the pollen from several individuals & always with the same result I do not think the species can be dimorphic.⁷

Only 3 plants of your Plumbago are alive, but they are doing well. Hundreds of y^r Gesnera have germinated.⁸ Kuhn announces in the Bot. Zeitung that he is going to publish a work on dimorphic plants of all kinds, but as far as I can judge, he does not experiment, & therefore will not interfere with me.⁹

I dare say your observations in crossing orchids will be very interesting; they already illustrate most of the leading laws; but I fear their interest will be greatly lessened by the crossed seeds not germinating. One single man in Europe has found out how to make these seeds germinate, & he keeps it a secret in his trade of nurseryman.¹⁰ He also has made some strange crosses between distinct genera, & these hybrids have flowered.

D^r Hooker tells me that they have in vain tried at Calcutta to make the seeds of hybrids germinate;¹¹ yet American orchids growing in the Bot. Garden there have spontaneously sown themselves and grown on adjoining trees.

I presume this strange difficulty in making the seeds germinate explains their astonishing number, which you and others have shewn.¹² I am not able to do much this summer in experimenting as all my time is taken up in getting my book thro’ the press;¹³ it progresses very slowly & is I fear hardly worth the great labour it costs me.

With cordial thanks for your never failing kindness I remain my dear Sir | yours very sincerely | Ch. Darwin